At present various types of conductive hoses are known in which the conductive layer may be positioned either on the inside (in contact with the fluid conveyed) or on the outside (in contact with the external environment).
For example, patent EP 707 169 refers to a hose in which a conductive layer of plastic or elastomeric material covers an inner layer which forms the duct for the fluid, and in which a narrow electrically-conductive strip extends longitudinally along the hose. Moreover, said strip is at least partly in contact with the conductive layer and is homogeneously inserted in a spiral shape in the film which forms the inner layer.
Patent EP 999 396 refers to an antistatic hose with a wall made of elastomeric materials to which conductive particles are added. In this case the hose has a thin outer layer which is not conductive and which covers the conductive wall, except for a spiral portion.
However, the conductive hoses currently used have several disadvantages.
It should be remembered that the hoses are often used in systems together with moving parts. Therefore, the hoses have to be moved over the floor by dragging (in particular when hoses are full of product they are very heavy).
Despite the fact that in most applications the floors are smooth, hoses with an outer surface made of elastomeric material tend to wear due to friction. This phenomenon is particularly evident in the case of dark coloured hoses when they are dragged, leaving a coloured mark on the floor.
The wear phenomenon is aggravated by the fact that the elastomeric material adheres well to the ground, increasing friction.
This disadvantage is particularly problematic in those production environments (such as in the pharmaceutical and/or food industry) in which cleanliness is essential.
Moreover, hoses made of elastomeric material cannot resist all chemical attacks. As a result, the hoses should be used in environments in which they come into contact with a single product or with two or more products of a similar chemical nature.
Secondly, the use of elastomeric materials for hoses built on a mandrel, makes the hose difficult to clean, due to the fact that the surface is not smooth because of the cloth finish.